A circuit arrangement of this type is known from DE-OS 27 43 954.
It often happens, particularly when a circuit arrangement of this type is used for measuring waste water which flows through a tube element, that the tube element is not completely filled. A siphon is required in order to ensure that the tube element becomes and always remains completely full. However, the disadvantage of a siphon of this type is that additional flow resistance is created for the liquid and that, furthermore, substantial construction costs are involved in producing the siphon, particularly in the case of very wide tube elements.
It is known to provide several electrode pairs, by means of which a separate additional measurement of the level of liquid in the tube element can be made. However, an additional liquid level measurement of this type is expensive.